Created attachment 568615 [details]
blockedDesigner.png

Description of problem:
In Firefox, pop-ups are blocked by default. In case the user has not yet allowed pop-ups for Guvnor's host and tries to view a process version diff, error message is displayed and designer's workspace is blocked forever. There is no way to cancel the operation. The only way to continue editing the process is to close the process and open it again. Fortunately, any unsaved work can be saved.

Version-Release number of selected component (if applicable):
BRMS 5.3.0 ER4

How reproducible:
if pop-ups are blocked for Guvnor's host (is default in Firefox)

Steps to Reproduce:
1. make sure pop-ups are blocked and exception for localhost has not been added yet
2. access designer by opening any BPMN2 process or by creating a new one in Guvnor
3. if you have just created the process, save it first so that at least one version is checked in
4. try viewing any version diff, the result should match the attached screenshot
  
Actual results:
"Creating diff..." progress message never disappears and blocks the designer workspace forever

Expected results:
option 1) In case of failure to view the diff (popup is blocked) the progress message should disappear so that user can dismiss the error message and continue working with designer

option 2) don't use pop-ups to view the diff, use HTML the same way it is used to view BPMN2 or JSON source of the process

Additional info: